EP1074369B1 - Method for manufacturing highly stressed composite pieces - Google Patents

Abstract

Composite articles are produced by impregnating a parallel array of reinforcing fibers with a resin, partially polymerizing the resin with ionizing radiation, cutting the resulting precomposite into lengths, stacking the lengths on a nonplanar support so that they conform to the shape of the support, and molding the stack under pressure to complete the polymerization of the resin. Independent claims are also included for the following: (1) a nonplanar multilayer composite material comprising parallel reinforcing fibers in a matrix of radiation-curable resin, where: each fiber is contained within a single layer; each layer is less than 0.3 mm thick; the matrix has a glass transition temperature (Tg) above 150 degrees C; and the material has a Shore D hardness of more than 80; (2) a precomposite of great length with a thickness of less than 0.3 mm comprising parallel reinforcing fibers in a matrix of radiation-curable resin and coated with a protective film that is opaque to ultraviolet-visible radiation, where the matrix has a Tg of 40-130 degrees C and the precomposite has a Shore D hardness of 50-65.

Description

The present invention relates to processes for manufacturing composite parts, in particular in the case of pieces of complex shapes. It relates more particularly to coins composites very strongly mechanically stressed.

A process for manufacturing composite parts consists in molding a dough by compression under high pressures and complete polymerization before demolding. The dough has been prepared previously, and comprises a mixture of resin and short fibers. This process is very widely used because of its ability to manufacture complex shaped parts and its high productivity. However, the compression molding process is incompatible with the use of long reinforcing fibers. For this reason, we can not consider achieve by this process the most mechanically stressed parts

Other techniques are known that make it possible to use reinforcing fibers long. One of these techniques is called "pultrusion". It involves unwinding the fibers of unlimited length, and immerse them in a bath of resin to ensure impregnation. Then they are pulled through a heated die, then through a heated chamber where the polymerization is carried out. This way you can continuously pull section products whatever, dictated by the shape of the die. But it's always about straight products. Another known technique is the filament winding. On a mandrel that is mobile in rotation and translation, winding sets of prepreg reinforced fibers. The manufactured object is polymerized in an oven. We get tubes, or large parts like tanks. But besides the fact that the variety of forms is very restricted, it is difficult to rigorously position the fibers in the thickness of the fabricated wall. These have tendency to get closer to the surface of the mandrel. It is also difficult to maintain a proportion of fibers constant throughout the thickness of the wall.

It is also known molding techniques of parts made of composite, including use of a preform, itself molded, to facilitate the placement of the fibers of enhancement. It has been proposed in patent EP 0 655 319 and in GB-A-1,522,441 to stabilize a resin preform having reinforcing fibers by heating the preform to obtain a consistency pasty, whose viscosity still allows a compression molding. Then we unmold pasty preform and is put in place in a second mold heated to a higher temperature high, in order to perform a compression molding of the pasty preform while performing the polymerization.

However, the problem of such treatment is that it is difficult to control the stage at which bring what we will call a "prepolymerization" (initial polymerization partial). However, it is necessary to reach a sufficient consistency for the subsequent manipulations do not cause too much disorganization in the positioning of the fibers. Of course no longer prepolymerization is advanced and the fibers are better maintained, but the more difficult it becomes to change the shape during the subsequent molding of the preform. Moreover, it is also very difficult, even almost impossible, to interrupt this process of polymerization, which can sometimes be very fast because of the exothermic reaction. In this case, the stiffness of the resin reinforced becomes quickly too important, which is incompatible with a subsequent molding.

Thus, except for composite parts of flat shape or bar or rectilinear tube, or for other simple forms, we have not managed to position long fibers exactly in the correct orientation and in a properly controlled density throughout the thickness of the room. It may be noted that, in the aforementioned patent, the fibers are cut to facilitate their implementation. This results in an inevitable degradation of the effect of enhancement. "Long fiber" or "long fiber" or "fiber of infinite length "of fibers whose length is limited only by the dimensions of the part, or at least by the dimensions of the parts of the room that need to be reinforced, without this length is limited by constraints from the method of implementation. We hear by "position individually" the fact of starting yarns or simple flat fabrics, and not of three-dimensional fabrics that are each time specific to a single fabricated piece and that also pose significant handling problems.

The object of the invention is to provide a method for manufacturing parts composites without degradation of the maximum possible reinforcing effect depending on the fibers selected, and which is applicable to a wide variety of shapes, including radii of curvature very small. In order to reach the most complex forms and also in some cases to can marry the composite structure with other materials like rubber, another objective is to be able to introduce the constituents of the composite part into an open mold, as a mold for tires, which in practice excludes injection techniques. The invention aims to propose a manufacturing technique that meets the objectives mentioned above and which lends itself to the mechanization and rapid rates sought for industrial manufactures.

• disposer lesdites fibres de renforcement sensiblement parallèlement à un plan et les imprégner de ladite composition;
• exposer la composition contenant lesdites fibres, en couche d'épaisseur inférieure à ladite épaisseur donnée, à un rayonnement ionisant, pour polymériser partiellement la résine, l'exposition à un rayonnement ionisant étant arrêtée après que l'indice D constitué par la dureté Shore D du précomposite divisée par la dureté Shore D du composite final ait atteint une valeur de l'ordre de 0.5 et avant que ledit indice D ait atteint une valeur de l'ordre de 0.7 et obtenir un précomposite dans lequel ladite composition est en phase solide ;
• prélever des tronçons dans le précomposite et les appliquer sur un support, dont la surface est de forme non plane, en les empilant les uns sur les autres en nombre dicté par ladite épaisseur donnée, et en leur faisant épouser intimement ladite forme du support et ainsi créer un empilage de tronçons contraints ;
• soumettre l'empilage à un moulage final sous une pression et à une température appropriées afin de poursuivre la polymérisation de la résine et de solidariser les différents tronçons de précomposite.

The subject of the invention is a process for manufacturing composite parts of given thickness, comprising reinforcing fibers parallel to at least one preferred reinforcing direction, said fibers being embedded in a matrix based on a composition comprising a hardenable resin. by ionizing radiation, the method comprising the following steps:

• arranging said reinforcing fibers substantially parallel to a plane and impregnating them with said composition;
• exposing the composition containing said fibers, in a layer of thickness less than said given thickness, to ionizing radiation, to partially polymerize the resin, the exposure to ionizing radiation being stopped after the index D consisting of the Shore D hardness precomposite divided by the Shore D hardness of the final composite has reached a value of the order of 0.5 and before said index D has reached a value of about 0.7 and obtain a precomposite wherein said composition is in the solid phase;
• collecting sections in the precomposite and applying them on a support, the surface of which is of non-planar shape, stacking them on top of one another in a number dictated by said given thickness, and intimately marrying said shape of the support and thus create a stack of constrained sections;
• subjecting the stack to a final molding under a pressure and at an appropriate temperature in order to continue the polymerization of the resin and to secure the different sections of precomposite.

The process is more particularly directed to the use of fibers of infinite length. We start from spun comprising in general a large number (of the order of one hundred) of filaments elementals with a diameter of a few microns, these filaments being all side by side, so substantially parallel to each other, with some overlaps. If it is indeed impossible to guarantee filament storage absolutely perfectly in parallel, we want to indicate the expression "substantially parallel to a plan" that it is not a cable or a braid and that the filaments are arranged parallel to the geometric precision of the arrangement close. The preferred reinforcement direction is, for example, the direction of tensile stresses in the part to be manufactured. But we can also start from a ribbon or a fabric having not only fibers oriented parallel to each other, called warp yarns, that is oriented in said preferred direction, and further containing other fibers, constituting for example weft son, regardless of the density.

The step of impregnating the fibers is not in itself specific to the present invention, the man the profession can easily select any suitable method, the impregnation being precede or follow the phase of arrangement of the fibers parallel to a plane. Arrange the fibers parallel to a plane is intended that, at the latest, while one starts the polymerization of the resin, the reinforcing fibers are appropriately ordered to they are, in the final composite room, judiciously arranged to provide fully the reinforcing effect.

By "precomposite" is meant a material whose resin is prepolymerized to form a solid medium (so-called gelation step or beyond), so that the precomposite has a sufficient cohesion to be able to be installed in an open mold, with the solicitations this assumes, without risking a "spinning" of the fibers during which the rate of resin of the preform would decrease in a non-controlled way. The purpose of prepolymerization is therefore to achieve a minimum level of polymerization to avoid any flow of resin during further processing thereof (in fact, a treatment of the composite or article in which it will be incorporated) under the action of the temperature, even under the action of the pressure. The purpose of prepolymerization is also to achieve a minimum level of polymerization to give the precomposite resistance to buckling of its fibers during a bending as imposed by the application step on a non-planar support.

The polymerization triggered by ionizing radiation not only achieves this stage, but also allows to stop the polymerization process by ceasing to issue said radiation. Indeed, the goal of prepolymerization is still not to exceed a level maximum of polymerization, allowing the bonding of the precomposite either on itself or on rubber as will be explained in detail later.

Prepolymerization as proposed, associated with an implementation of the material by stratification in sufficiently thin layers, allows to reconstitute a block of form and any thickness, with respect to a monolithic material prepared with the same resin and the same fibers in identical density, prepared for example by pultrusion.

As suitable ionizing radiation, it is proposed to use radiation in the spectrum ranging from 300 nm to 450 nm, or an accelerated electron beam.

For example, a precomposite is prepared in a ribbon approximately 0.1 mm thick (width whatever, chosen rather according to the part to be manufactured), and the piece made from stretches of this ribbon has the same properties as a monolith, ie a piece of simple form which is not constituted by stratification and superposition of thin layers. In in other words, we do not observe degradation of the properties which are those due to the resin chosen and especially due to the chosen reinforcement fiber. Note that when stacking, nothing precludes crossing the fibers from one section to another, depending on the reinforcing effect referred to for the composite part to be manufactured. This is a design parameter of the part Composite on which we will not return in the sequel, but which enters the field of the invention.

According to an advantageous embodiment of the invention, during the application of the sections on said support, stresses are exerted on said sections of precomposite in order to force them to to intimately marry the said form of support. Preferably, the surface of the support against which the stacks are stackable; it is easier to intimately marry them area. Preferably, the deformation stresses are maintained on said sections of precomposite at least until the beginning of the heat treatment step.

It is on the one hand the state of prepolymerization reached, perfectly controlled thanks to a prepolymerization by ionizing radiation, and on the other hand the subdivision into several layers of thin, which allow at the same time to impose enough bending radii small without significant residual stresses within each section, without any buckling of the fibers during stacking, and without the result of dispersions of fibers in the cross section of the stack, including dispersions in thickness. The elastic return of the stacks thus made to a configuration in which the internal stresses would be zero is relatively small, which allows quite easily mechanically maintain or freeze the deformation imposed without hindering the subsequent stages of completion of the final composite part.

Initiating the polymerization of the resin in a very thick layer less than the thickness of the final composite part facilitates the deformations mentioned above. Considering the minimum radius of curvature "r" of said composite part, the beginning of the polymerization is advantageously carried out in thick layer "e" such that "e" is smaller than "r" divided by 20. Preferably, and in particular to facilitate the temporary maintenance of the deformed state before the rest of the process freezes definitively the structure of the final product, the beginning of the polymerization is carried out in layer of thickness "e" such that "e" is smaller than "r" divided by 150.

• la figure 1 est un schéma partiel d'une installation mettant oeuvre une première phase du procédé selon l'invention ;
• la figure 2 est un schéma illustrant une phase ultérieure du procédé selon l'invention appliqué à la réalisation d'une pièce composite ;
• la figure 3 est un schéma illustrant la phase suivant celle illustrée à la figure 2;
• la figure 4 est un schéma illustrant une phase ultérieure du procédé selon l'invention appliqué à la réalisation d'une pièce lamifiée comportant à la fois une pièce composite et du caoutchouc ;
• la figure 5 est un schéma illustrant la phase suivant celle illustrée à la figure 4.

Two examples of implementation of the method according to the invention will now be described with the aid of the following appended figures:

• Figure 1 is a partial diagram of an installation implementing a first phase of the method according to the invention;
• Figure 2 is a diagram illustrating a subsequent phase of the method according to the invention applied to the production of a composite part;
• Figure 3 is a diagram illustrating the phase following that illustrated in Figure 2;
• Figure 4 is a diagram illustrating a subsequent phase of the method according to the invention applied to the production of a laminated part comprising both a composite part and rubber;
• FIG. 5 is a diagram illustrating the phase following that illustrated in FIG. 4.

FIG. 1 shows a bobbin 10 containing a yarn 11 which, in the illustrated example, consists of by fiberglass. An impregnation device 20 having a tank 21 containing a composition based on a curable resin and a photoinitiator suitable for the radiation by which said composition will be treated. The device of impregnation 20 comprises an impregnating chamber 22. There emerges a prepreg 12 which is introduced into a prepolymerization device 30, in which the prepreg 12 is prepolymerized by ionizing radiation, the treatment being carried out protected from oxygen. As for the radiation 31 to which the composition is exposed, its wavelength is typically less than 450 nanometers, preferably between 300 nm and 450 nm. We can example use an ultraviolet lamp. Rollers 40 result in the obtained precomposite 13 in the direction of the arrow F. Finally, a shear 50 can take sections 14 in the precomposite manufactured continuously, to implement them as explained below.

Then comes the implementation phase of the sections 14 of precomposite. In Figure 2, we see a support 61 whose shape makes it possible to manufacture a "C" shaped object (for example a C-shaped spring). The sections 14 of precomposite are deformed (see arrows D in FIG. 2) to make them marry the shape of the support 61. The sections are arranged on the support 61 so that the fibers are parallel to the plane of FIG. 2, traveling from one end of the object to the other in C.

The level of prepolymerization must be high enough to allow stacking of sections 14 on the desired support without causing buckling of the fibers 11 located inside of the curvature of the section 14 deformed, and to prevent the resin-based composition from becoming spread outside of the precomposite during the deformation, and also during a treatment subsequent thermal under pressure. This level of prepolymerization must however be low enough that the continuation of the polymerization of a stack of several sections of this precomposite under the combined effect of temperature and pressure creates through the interface between two adjacent sections of precomposite, in order to obtain a composite material having excellent mechanical properties, in particular flexural and in shear.

It is proposed to experimentally control the level of prepolymerization by means of a analysis of the Shore D hardness of the precomposite. Shore hardness values given below are measured with a Shore D durometer as described in standard NF T 46-052. Exposure to ionizing radiation is preferably stopped for example after the hardness Shore D of the precomposite became greater than 45 and before the Shore D hardness of the precomposite is greater than 65 if the Shore D hardness of the order of 90 to 95 is final composite. More generally, it is proposed that the step of exposure to radiation ionizing is stopped after the index D constituted by the Shore D hardness of the divided precomposite by the Shore D hardness of the final composite has reached a value of the order of 0.5 and before said index D has reached a value of the order of 0.7.

The level of prepolymerization can also be experimentally controlled by means of an analysis of the glass transition temperature T _g of the composition of the precomposite. It is proposed a rule of good practice that, considering the index T = T _gf -T _gpr , T _gpr being the glass transition temperature of the composition of the precomposite and T _gf being the glass transition temperature of the composition of the composite Finally, the exposure to ionizing radiation is stopped after the index T has become less than 120 ° C and before said index T has become less than 30 ° C. For example, in the case where the glass transition temperature T _g of the composition of the final composite is of the order of 160 ° C, the exposure to ionizing radiation is stopped after the glass transition temperature T _g of the composition of the precomposite has reached a value of the order of 40 ° C and before the glass transition temperature T _g of the composition of the precomposite has reached a value of the order of 130 ° C.

In passing, it can be noted that the prepolymerization level of the precomposite is such that that one is beyond the point of gelling of the resin. The level of prepolymerization is achieved by adapting, for example, the treatment time to ionizing radiation (speed of travel imposed by the rollers 40, length of the prepolymerization device 30).

To marry the shape of the surface of the support 61 with precomposite, it is possible to envisage the following possibilities. Either said sections 14 of precomposite are stacked and deformed individually (see arrows D in Figure 2) to make them each marry successively the form of the support 61. Either said sections 14 of precomposite are stacked and deformed by groups of several, or all together, to make them collectively marry the shape of the support 61.

In all cases, although the nerve of the sections 14 is rather weak, it is necessary to make sure that that the stack of sections of precomposite keeps a shape in C, at least enough for allow the implementation of the following steps. Provisionally, the each other the different sections 14 of the stack by interposing at least partially a layer 15 of said composition, for example at the ends of the C and at the surface of one least sections to maintain on top of each other, as shown in Figure 2. Just expose at least partially said layer 15 to ionizing radiation, for example radiation ultraviolet - visible, even through sections 14 as shown schematically in Figure 2, for partially polymerize the resin of said layer 15. Of course, as long as the connection between adjacent sections described above is not performed, or more generally as long as, whatever is the way, we did not make sure that the sections are spontaneously maintained at the imposed deformation, they must be maintained by externally applying the appropriate forces.

As a variant of the provisional joining of the various sections 14 by photoinitiation, it is possible to consider submitting the stack to a molding under pressure and at a temperature appropriate (eg of the order of 130 ° C) in order to continue at least partially the polymerization of the resin, before any other intermediate steps and before molding final. In another variant, it is conceivable to temporarily make one of the other different sections 14 of the stack by interposing a temporary holding layer essentially comprising a composition of high viscosity. Note that these different methods can also be used concomitantly.

Figure 3 shows the final step. A counter-mold 62 is brought over the support 61 coated with a stack 16 of sections 14 of precomposite. Final molding under pressure, for example of the order of 10 bars. The temperature during the molding under pressure is preferably greater than the glass transition temperature T _g of the composition of the precomposite. As an indication, a suitable treatment temperature is of the order of at least 150 ° C. The final properties of the material are not solely and not even primarily due to said prepolymerization. They also result largely from the heat treatment during this final molding step, which ensures excellent bonding of previously stacked sections on each other.

Thanks to the fact that the control of the degree of prepolymerization is not carried out by thermal, it is possible to adjust the viscosity of the composition during the impregnation step fibers by a moderate rise in the temperature of said composition. For example, we can heat up to about 80 ° C, without any significant effect on the stability of the resin. This allows a much better impregnation of the fibers. We can thus have a adjustment parameter of the impregnation phase independent of the parameters of the steps subsequent processes.

As for the suitable resins, by way of illustration, let us mention that the resin can be chosen in the group consisting of vinylester resins and unsaturated polyester resins, or can be an epoxy resin. And as for the reinforcing fibers, let's mention that they can be chosen from organic fibers such as high polyacrylic fibers tenacity or oxidized polyacrylonitrile fibers, high tenacity polyvinyl alcohol fibers, aromatic polyamide fibers or polyamide-imide fibers or polyimide fibers, chlorofibers, high tenacity polyester fibers or aromatic polyester fibers, fibers high tenacity polyethylene, high tenacity polypropylene fibers, cellulose fibers or rayon or high tenacity viscose, polyphenylene benzobisoxazole fibers, fibers polyethylene naphthenate, or they can be chosen from inorganic fibers such as glass fibers, carbon fibers, silica fibers, ceramic fibers (alumina, aluminosilicate, borosilicoaluminate). Preferably, the process uses fibers unidirectional parallel to said at least one preferred reinforcing direction, arranged substantially parallel during the impregnation with said composition.

The following table gives comparative results on different samples 1 to 5, prepared in medium of different resins. The prepared samples are parallelepipedic blocks 2 mm thick.

In all the examples (controls and samples), the reinforcing fibers are fibers of glass, of the type indicated. Under the column "preparation", "direct molding" means that one has prepared an equivalent monolith without any stratification; parallel fibers between them are regularly distributed in the resin matrix. All samples were final molded with heat treatment under pressure. Control 1 was prepared with a prepreg of unidirectional fibers, available commercially under the name Prepreg Vicotex (reference BE M10 / 29.5% / 25x2400 - P122 EPOXY 60 mm glass strip), consisting of unidirectional glass fibers embedded in an epoxy resin, manufactured by Hexcel Composites S.A .. The control 2 comprises yarns commercially available under the name PPG 2001 300Tex, embedded in a resin available commercially under the name Atlac 590. The control 3 is obtained by stacking 10 sections of precomposite, the precomposite having has been prepolymerized thermally. It has the same glass fibers embedded in the same resin as witness 2.

In all examples of implementation of the invention, the composition comprises a photograph polymerization initiator and the radiation is included in the ultraviolet - visible spectrum. In this case, preferably, a glass fiber is used.

All the samples of the invention are obtained by stacking 10 precomposite sections 0.2 mm thick, protected by two 50 micron nylon films. The precomposite was prepolymerized by exposure for the number of seconds indicated under ultraviolet-visible radiation (Philips UV Tube TLK 40W / 03) placed at a distance of 180 mm from the section. The precomposite proves to be sufficiently transparent to the radiations so that the prepolymerization is well homogeneous and for the temporary maintenance as set out above, in which the radiation treatment is carried out through an already prepolymerized section, to be effective. Resin Fiberglass Fiber rate Preparation curing Witness 1 Epoxy M10 Vetrotex RO 99 2400 P122 72 Direct molding 1 h at 120 ° C + 1h at 150 ° C Witness 2 Atlac 590 PPG 2001 300Tex 73 Direct molding 15 min at 120 ° C + 15 min at 165 ° C Witness 3 Atlac 590 PPG 2001 300Tex 74 Stacking 10 layers 15 min at 120 ° C + 15 min at 165 ° C Sample 1 Atlac 590 PPG 2001 300Tex 70 UV treatment for 30 seconds then stacking 10 layers 15 min at 165 ° C Sample 2 Heltron 970 PPG 2001 300Tex 68 UV treatment for 30 seconds then stacking 10 layers 15 min at 165 ° C Sample 3 RD903 + styrene PPG 2001 300Tex 72 UV treatment for 20 seconds then stacking 10 layers 15 min at 165 ° C Sample 4 RD904 + styrene PPG 2001 300Tex 69 UV treatment for 20 seconds then stacking 10 layers 15 min at 165 ° C Sample 5 Derakane 470-36S PPG 2001 300Tex 72 UV treatment for 20 seconds then stacking 10 layers 15 min at 165 ° C

The resins of Controls 2 and 3 and all samples are all vinyl ester resins. (Epoxy Vinyl Ester Resins). The supplier of ATLAC 590 resin is DSM - BASF Structural Resins. Note in passing that, as a variant of what was said in the preceding paragraph, it is possible to adjust the viscosity of said composition by adding a monomer copolymerizable with the resin and by varying the proportion. For example, the monomer whose proportion is styrene. The photoinitiator is bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide (Irgacure photoinitiator 819). The supplier of the resin "Heltron 970" is Ashland Chemical. The supplier of the "RD903" and "RD904" resins is UCB Chemicals. The Resin supplier "Derakane 470-36S" is Dow.

• une résine à base de bisphenol A, le bisphenol A apparaissant entre les crochets :
  
• une résine novolaque apparaissant entre les crochets :
  
• un monomère dont la proportion influence la viscosité, le styrène:
  

ATLAC 590 resin is an epoxy resin unsaturated by an unsaturated monocarboxylic acid (see formula below). This resin comprises:

• a resin based on bisphenol A, bisphenol A occurring between the hooks:
  
• a novolac resin appearing between the hooks:
  
• a monomer whose proportion influences the viscosity, styrene:
  

The following table illustrates the mechanical properties. Flexion Test Scars test Young's module Breaking stress Contrary rupture (MPa) (MPa) (MPa) Witness 1 40977 1374 78 Witness 2 37142 1145 83 Witness 3 28140 733 28

Witnesses 1 and 2 illustrate the best performance that can be expected from a monolith properly prepared. The mechanical performances of the samples are illustrated by the value of the Young's modulus, by the maximum stress at break of the sample in flexion test (Afnor Standard T57-302), and the maximum shear stress at break (Standard Afnor T57-303), this last property making it possible in particular to highlight the quality of the bonding between the layers of the control 3 and the sample according to the invention. We observed a significant degradation of the properties of the control 3, especially a degradation considerable amount of maximum shear stress at break. On the other hand, the invention makes it possible to find substantially the properties of the witness 2, which is a monolith directly comparable. The mechanical properties of the material are the same, as the sections of precomposite have been deformed or not.

The following table illustrates the partial polymerization treatment. It gives a qualitative description of the precomposite obtained for different values of the ultraviolet radiation treatment time. The samples concerned contain 70% by weight PPG 300 Tex glass fibers embedded in an Atlac 590 resin with 2% of Irgacure 819 photoinitiator. The precomposite is prepared in a 0.25 mm thick and 30 mm wide layer. glass fibers being unidirectional. The layer is surface protected by a 50 micron thick nylon film for irradiation. The irradiation is ensured by 2 Philips TLK 40W / 03 UV tubes placed at a distance of 180 mm from the layer to be treated. A stack of 15 sections of 30 mm of precomposite is then formed. The buckling strength is evaluated by manually winding a fiber-oriented sample onto a cylinder 30 mm in radius. The resistance is evaluated at a pressure of 30 bar at a temperature of 110 ° C. The Shore D hardness is measured according to the standard already indicated. UV exposure time (sec) Surface appearance Shore D hardness Resistance to buckling Resistance to pressure 10 poissant 20 many flamingos crushed composite, exuded resin 20 non-sticky 35 buckling crushed composite 25 non-sticky 45 little buckling composite not crushed 27 non-sticky 50 no buckling composite not crushed 30 non-sticky 65 no buckling composite not crushed 40 non-sticky 75 no buckling composite not crushed 60 non-sticky 80 no buckling composite not crushed

It can be seen that satisfactory results are obtained from a treatment time greater than 25 seconds. The irradiation step is preferably limited in time as soon as the hardness Appropriate Shore D has been reached, the reader being referred to explanations already provided.

The invention makes it possible to obtain an intermediate product constituted essentially by a precomposite prepared in great length and in a thickness of less than 0.3 millimeters, comprising reinforcing fibers parallel to at least one preferred reinforcing direction, said fibers being embedded in a matrix with base of a composition comprising an ionizing radiation curable resin, wherein the glass transition temperature T _g of the matrix is between 40 ° C and 130 ° C, and wherein the Shore D hardness of said precomposite is between 50 and 65, coated with a protective film opaque to ultraviolet - visible radiation. Thanks to the protective film, this intermediate product can be stored without the prepolymerization rate noticeably changing. It can be used on another site and implemented according to the indications of the method of the invention.

According to another particular aspect, the invention relates to a method of joining a composite material to rubber. The described method makes it possible to produce a laminate in which said composite parts are intimately secured to rubber. For this purpose and preferably, on the surface of each section intended to receive a layer of rubber, one deposits a layer of resorcinol formaldehyde latex (RFL) glue, said layer of RFL glue being dried without reaching a temperature above 100 ° C, ie without treatment heat at high temperature, before receiving said rubber layer. During molding final, we obtain a good solidarity of the sections of precomposite between them and between the composite elements and rubber.

The invention therefore also extends to a material in which, between some of said strata at less, is interposed a layer 17 of sulfur-vulcanizable elastomer composition. Advantageously, between at least some of said strata and said composition based on elastomer vulcanizable with sulfur, is interposed a layer of glue resorcinol formaldehyde latex (RFL).

FIG. 4 shows the support 61 first covered by two sections 14 of precomposite stacked, deformed and temporarily maintained by a layer 15 of the composition prepolymerized with ultraviolet radiation. The two strata thus deposited and pre-stabilized spontaneously preserve their C-shape. A layer 17 of a composition based on raw rubber is then deposited over the second section 14. Of course, the Rubber-based composition can marry without much difficulty the shape imposed on first layers of precomposite. Then we can continue stacking sections 14 of precomposite, with temporary maintenance of the deformed state. We can of course use all means described for Figure 2.

The final molding step, illustrated in FIG. 5, allows both the good bonding of the sections 14 between them, the vulcanization of the rubber, the complete polymerization of the resin and the bonding the rubber and the resin. A counter-mold 63 is brought over the support 61 coated with a stack 18 of sections 14 of precomposite with the interposition of a layer 17 of rubber. Final molding is carried out with heat treatment under pressure.

The use of an unpolymerized RFL glue, deposited on these sections of precomposite, does not use special elastomers to bond the rubber to the material composite.

Claims (36)

1. A process for manufacturing composite parts of given thickness, comprising reinforcement fibres (11) which are parallel to at least one preferred direction of reinforcement, said fibres being embedded in a matrix based on a composition comprising a resin which can be hardened by ionising radiation, the process comprising the following stages:

   arranging said reinforcement fibres substantially parallel to one plane and impregnating them with said composition;

   exposing the composition containing said fibres, in a layer of thickness less than said given thickness, to ionising radiation (31), in order partially to polymerise the resin, the exposure to ionising radiation being stopped once the index D constituted by the Shore D hardness of the precomposite divided by the Shore D hardness of the final composite has reached a value of the order of 0.5 and before the index D has reached a value of the order of 0.7, and to obtain a precomposite in which said composition is in the solid phase;

   taking lengths (14) from the precomposite and applying them to a support (61), the surface of which is non-planar in shape, by stacking them on one another in a number dictated by said given thickness, and by causing them to fit snugly against said shape of the support, and thus to create a stack of stressed lengths;

   subjecting the stack to final moulding at a suitable pressure and temperature to continue the polymerisation of the resin and to join the different lengths of precomposite.
2. A process according to Claim 1, in which the surface of the support is developable.
3. A process according to one of Claims 1 or 2, in which, considering a minimum radius of curvature "r" of said composite part, the start of prepolymerisation is effected in a layer of thickness "e" is such that "e" is smaller than r/20.
4. A process according to one of Claims 1 to 3, in which, considering the minimum radius of curvature "r" of said composite part, the start of polymerisation is effected in a layer of thickness "e" is such that "e" is smaller than r/150.
5. A process according to one of Claims 1 to 4, in which said lengths (14) of precomposite are stacked and deformed individually to make them each fit snugly in succession against said shape of the support.
6. A process according to one of Claims 1 to 5, in which said lengths (14) of precomposite are stacked and deformed in groups of several lengths to make them fit snugly collectively against said shape of the support.
7. A process according to one of Claims 1 to 6, in which the temperature during the moulding under pressure in the final moulding stage is higher than the glass transition temperature T_g of the composition of the precomposite.
8. A process according to one of Claims 1 to 7, in which the exposure to ionising radiation is stopped once the index T = T_gf - T_gpr, T_gpr being the glass transition temperature of the composition of the precomposite and T_gf being the glass transition temperature of the composition of the final composite, has become less than 120°C and before said index T has become less than 30°C.
9. A process according to one of Claims 1 to 8, in which the stage during which said composition is exposed to ionising radiation is carried out with oxygen excluded.
10. A process according to one of Claims 1 to 9, in which, during the application of the lengths (14) to said support (61), stresses are exerted externally on said lengths of precomposite in order to force them to fit snugly against said shape of the support, and said stresses are kept exerted externally at least until the start of the heat treatment stage.
11. A process according to one of Claims 1 to 9, in which the different lengths of the stack are made temporarily integral with each other by inserting at least in part a layer (15) of said composition, and by exposing said inserted layer, at least in part, to ionising radiation, in order to prepolymerise the resin of said inserted layer.
12. A process according to one of Claims 1 to 9, in which the different lengths of the stack are made temporarily integral with each other by subjecting the stack to premoulding at a suitable pressure and temperature in order to continue the polymerisation of the resin, at least in part, before any other intermediate stages and before the final moulding.
13. A process according to one of Claims 1 to 9, in which the different lengths of the stack are made temporarily integral with each other by inserting a temporary holding layer comprising essentially a high-viscosity composition.
14. A process according to one of Claims 1 to 13, in which the viscosity of said composition is adjusted, during the stage of impregnation of the fibres, by increasing the temperature of said composition.
15. A process according to one of Claims 1 to 14, in which the resin is selected from the group consisting of unsaturated vinylester resins and polyester resins.
16. A process according to one of Claims 1 to 14, in which the resin is an epoxy resin.
17. A process according to Claim 15, in which said composition comprises a monomer which can be copolymerised with the resin and the viscosity of said composition is adjusted by varying the proportion of monomer.
18. A process according to Claim 17, in which said monomer is styrene.
19. A process according to one of Claims 1 to 18, in which said composition comprises a polymerisation photoinitiator and the radiation (31) lies within the visible ultraviolet spectrum.
20. A process according to Claim 15, in which said composition comprises a polymerisation photoinitiator which is bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and the radiation (31) lies within the visible ultraviolet spectrum.
21. A process according to one of Claims 1 to 18, in which the reinforcement fibres (11) are selected from the group comprising high-tenacity polyacrylic fibres, oxidised polyacrylonitrile fibres, high-tenacity polyvinyl alcohol fibres, aromatic polyamide fibres, polyamide-imide fibres, polyimide fibres, chlorofibres, high-tenacity polyester fibres, aromatic polyester fibres, high-tenacity polyethylene fibres, high-tenacity polypropylene fibres, cellulose fibres, rayon fibres, high-tenacity viscose fibres, polyphenylene benzobisoxazole fibres, polyethylene naphthenate fibres, glass fibres, carbon fibres, silica fibres or ceramic fibres.
22. A process according to one of Claims 19 or 20, in which a glass fibre is used.
23. A process according to one of Claims 1 to 22, in which a layer (17) of composition based on sulphur-vulcanisable elastomer is interposed between some of the lengths of precomposite.
24. A process according to Claim 23 in which, on the surface of each length intended to receive a layer of composition based on sulphur-vulcanisable elastomer, there is deposited a layer of resorcinol formaldehyde latex glue (RFL), said layer of RFL glue being dried without reaching a temperature of greater than 100°C before receiving said layer of composition based on sulphur-vulcanisable elastomer.
25. A process according to one of Claims 23 or 24, in which the final moulding stage makes it possible to do all of: join the layers of the stack, to vulcanise the composition based on sulphur-vulcanisable elastomer, to polymerise the resin completely and to join the composition based on sulphur-vulcanisable elastomer and the resin.
26. A process according to one of Claims 1 to 25, using unidirectional fibres parallel to the said at least one preferred direction of reinforcement, arranged substantially parallel during impregnation by said composition.
27. A process according to one of Claims 1 to 26, in which the step consisting of exposing the composition obtaining a precomposite and [sic] carried out until a minimum level of polymerisation is obtained which makes it possible to impart to the precomposite a resistance to buckling of its fibres upon bending such as imposed by the stage of application on a support of non-planar shape and stopped so as not to exceed a maximum level of polymerisation permitting the gluing of the precomposite on to itself.
28. A precomposite prepared in a great length and in a width of less than 0.3 millimetres, comprising reinforcement fibres which are parallel to at least one preferred direction of reinforcement, said fibres being embedded in a matrix based on a composition comprising a resin which can be hardened by ionising radiation, in which the glass transition temperature T_g of the matrix is between 40°C and 130°C, and in which the Shore D hardness of this precomposite is between 50 and 65, coated with a protective film opaque to visible ultraviolet radiation.
29. A precomposite according to Claim 28, in which the resin is selected from the group consisting of unsaturated vinylester resins and polyester resins.
30. A precomposite according to Claim 28, in which the resin is an epoxy resin.
31. A precomposite according to Claim 29, in which said composition comprises a monomer which can be copolymerised with the resin.
32. A precomposite according to Claim 31, in which said monomer is styrene.
33. A precomposite according to one of Claims 28 to 32, in which said composition comprises a polymerisation photoinitiator and the radiation (31) lies within the visible ultraviolet spectrum, and in which the coating is opaque to visible ultraviolet radiation.
34. A precomposite according to Claim 29, in which said composition comprises a polymerisation photoinitiator which is bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and the radiation (31) lies within the visible ultraviolet spectrum.
35. A precomposite according to one of Claims 28 to 34, in which the reinforcement fibres (11) are selected from the group consisting of glass fibres and carbon fibres.
36. A precomposite according to one of Claims 28 to 35, in which the reinforcement fibres (11) are unidirectional fibres.

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